The present invention relates to a boost-type switching regulator and a semiconductor device for the boost-type switching regulator.
A boost-type switching regulator includes a boost-type DC-DC converter (a boost converter) using a chopper method. When a direct current is input into the boost-type DC-DC converter, a switching element of the boost-type DC-DC converter divides the direct current into a pulse electrical current. Then, the boost-type DC-DC converter is configured to obtain a direct current having a required voltage through combining the pulse electrical current.
The boost-type DC-DC converter is formed of the switching element, an inductor (a choke coil), a capacitor, a diode, and a control circuit for controlling an on-off of the switching element. In general, the switching regulator has an advantage of a high power conversion ratio about 80-98%. Accordingly, when the switching regulator is used as a power conversion circuit, it is possible to reduce power consumption and an amount of heat generation.
Patent Reference 1 has disclosed a conventional switching regulator. The conventional switching regulator includes an error amplifier unit; a converter; a driving unit; and a clamp circuit.    Patent Reference 1: Japanese Patent Publication No. 2009-136064
In the conventional switching regulator disclosed in Patent Reference 1, the error amplifier unit is configured to compare an output voltage of the conventional switching regulator with a reference voltage, so that the error amplifier unit generates an error signal according to an error of the output voltage relative to the reference voltage. The converter is configured to compares the error signal transmitted from the error amplifier unit with a detection signal according to a coil electrical current flowing through an output inductor of the conventional switching regulator, so that the converter outputs an off signal having a specific level when a value of the detection signal reaches a value of the error signal.
Further, in the conventional switching regulator disclosed in Patent Reference 1, the driving unit is configured to turn off the switching element when the off signal becomes a specific level, and to turn on the switching element when a clock signal is changed to a specific level. The clamp circuit is configured to clamp the error signal transmitted from the error amplifier unit at a clamp value according to the output voltage of the conventional switching regulator.
Patent Reference 2 has disclosed a conventional direct current conversion circuit. The conventional direct current conversion circuit includes a microprocessor; an induction element; a transistor; a hysteresis comparator; and a logic circuit.    Patent Reference 2: Japanese Patent Publication No. 2012-10581
In the conventional direct current conversion circuit disclosed in Patent Reference 2, the hysteresis comparator is configured to compare an output signal of the conventional direct current conversion circuit with a first reference potential or a second reference potential. The logic circuit is configured to calculate an output signal of the hysteresis comparator and a clock signal of the microprocessor. The transistor is configured to control an electrical current flowing through the induction element according to an output signal of the logic circuit, so that the transistor generates the output signal of the conventional direct current conversion circuit according to an electrical current flowing through the induction element.
In the conventional boost-type switching regulator, there may be a control method, in which a duty of a gate signal for driving the switching element is fixed. In the control method, when the output voltage thus detected is smaller than a target voltage, the gate signal is supplied to the switching element. Further, when the output voltage thus detected is greater than the target voltage, the gate signal is not supplied to the switching element. With the control method, it is possible to reduce a circuit size as opposed to, for example, a PWM-type switching regulator, in which a pulse width of a gate signal is controlled according to an output voltage.
In general, regardless of the control method, the conventional switching regulator is configured to finely divide the direct current with the switching element. Accordingly, the output voltage of the conventional switching regulator tends to have a relatively large ripple. When the conventional boost-type switching regulator is operated in the control method, in which the duty of the gate signal is fixed, it may be configured such that a sufficient off period of the switching element is secured to reduce the ripple generated in the output voltage. However, in this case, it may be difficult to obtain the output voltage with a desired level, thereby making it difficult to reduce the ripple.
In view of the problems described above, an object of the present invention is to provide a boost-type switching regulator and a semiconductor device for the boost-type switching regulator capable of solving the problems of the conventional switching regulator. In the present invention, it is possible to reduce the ripple generated in the output voltage of the boost-type switching regulator.
Further objects and advantages of the invention will be apparent from the following description of the invention.